Joint fusion implant and methods

ABSTRACT

An implant for fusing a joint between first and second bone portions. The implant includes a screw member, and a washer polyaxially rotatable relative to the screw member. The screw member includes a head, a lag zone, and a threaded engagement zone. The implant includes a fusion zone for joint compression, extending from the washer to the proximal end of the engagement zone. Fenestrations may be present in the fusion zone. The length of the fusion zone ranges from about 10 mm to about 37 mm. Different surface finishes including roughened and non-roughened may be applied selectively to selected portions of the implant. In an embodiment, the joint is a sacro-iliac joint, and upon implantation the implant extends from the exterior of the ilium, across the joint and into the sacral vertebral body. Instrumentation and methods for preparing the joint and implanting the implant are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of:

U.S. Non-Provisional patent application Ser. No. 15/420,849, filed Jan.31, 2017, entitled JOINT FUSION IMPLANT AND METHODS, which is pending;

U.S. Non-Provisional patent application Ser. No. 15/420,849 is acontinuation-in-part of:

U.S. Non-Provisional patent application Ser. No. 15/137,804, filed Apr.25, 2016, entitled JOINT FUSION INSTRUMENTATION AND METHODS, which ispending; and

U.S. Non-Provisional patent application Ser. No. 15/137,848, filed Apr.25, 2016, entitled JOINT FUSION INSTRUMENTATION AND METHODS, whichissued as U.S. Pat. No. 9,833,321 on Dec. 5, 2017.

The above-identified documents are hereby incorporated herein byreference.

STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINTINVENTOR

William W. Cross III is the inventor of the subject matter of U.S.patent application Ser. No. 14/790,480, filed on Jul. 2, 2015 andentitled SACROILIAC JOINT FUSION SCREW AND METHOD, published as U.S.Patent Application Publication no. US2016/0000488A1. William W. CrossIII is an inventor of the subject matter of the present disclosure. Theabove-identified patent application publication is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates to implants and methods for joint fusion.More specifically, the invention relates to implants, instrumentationand methods for fusing a sacroiliac joint.

The sacroiliac (SI) joints are formed by the connection of the sacrumand the right and left iliac bones. While most of the spinal vertebraeare mobile, the sacrum is made up of five vertebrae that are fusedtogether and do not move. The iliac bones are the two large bones thatmake up the pelvis. As a result, the SI joints connect the spine to thepelvis, and form the largest axial joints in the body. The sacrum andthe iliac bones are held together and supported by a complex collectionof strong ligaments. There is relatively little motion at the SI joints;there are normally less than 4 degrees of rotation and 2 mm oftranslation at these joints. Most of the motion in the area of thepelvis occurs either at the hips or the lumbar spine. These jointssupport the entire weight of the upper body when it is erect, placing alarge amount of stress across them. This can lead to wearing of thecartilage of the SI joints. Some causes of degeneration and/or pain inthe SI joints include osteoarthritis, pregnancy, leg length discrepancy,gout, rheumatoid arthritis, psoriatic arthritis, reactive arthritis, andankylosing spondylitis.

Treatment options have been limited to conservative care involvingphysical therapy and joint injections or traditional open SI jointarthrodesis surgery until recently. Open arthrodesis procedures reportedin the literature require relatively large incisions, significant boneharvesting, and lengthy hospital stays; moreover, they may requirenon-weight bearing for several months.

The systems and methods for sacroiliac joint fusion disclosed here canbe used to provide SI joint arthrodesis in a minimally invasiveprocedure. SI joint fusion using the systems and methods disclosedherein may provide advantages which can include a small incision,relatively short operating time with fewer steps, minimal blood loss,and a relatively short period of postoperative immobilization. Forexample, the steps disclosed herein for creating a cavity in the joint,filling it with graft material, and inserting a fusion device, may allbe accomplished through a single access cannula in a single procedure.The size and configuration of the cutting instrument allows insertioninto a bone or joint through a relatively narrow pathway, and creationof an undercut cavity within the bone or joint. Due to the shape andrigid construction of the blade disclosed herein and its assembly withinthe cutting instrument, the bone cutting instrument disclosed herein maycreate a cleaner cavity in a relatively short time, without the need toswitch out blade members or employ multiple cutting instruments.Implants for joint fusion are disclosed herein, including an embodimentfor SI joint fusion having a design which is based on specificanatomical measurements of the ilium, sacrum, and SI joint space. Anembodiment of the implant includes a fusion zone specifically sized tospan the SI joint and provide compression for long-term joint fixation,and a threaded engagement zone specifically sized to extend to andanchor in the body of the sacral vertebra.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1 illustrates a cross-sectional view of a natural sacroiliac jointand a cavity extending across the joint, the cavity filled with bonegraft material, and the joint fused by a fusion device comprising ascrew member and a washer, and a supplementary screw;

FIG. 2A illustrates a front view of a cutter which may be used to createthe cavity of FIG. 1, the cutter having a blade in a retractedconfiguration; FIG. 2B is a side view of the cutter of FIG. 2A, the sideview rotated 90 degrees from the front view; FIG. 2C is a side view ofthe cutter of FIG. 2A, with the blade in an extended configuration;

FIG. 3 is a partially exploded view of the cutter of FIG. 2A, the cutterincluding a handle assembly, a blade assembly, and an outer tube;

FIG. 4A is a front view of a blade shaft of the cutter of FIG. 2A; FIG.4B is a side view of the blade shaft of FIG. 4A; FIG. 4C is across-sectional view of the blade shaft of FIG. 4B, taken along line A-Ain FIG. 4B;

FIG. 5A is a partially exploded side view of one end of a blade shaftassembly for the cutter of FIG. 2A, the assembly having a blade shaft, ablade holder, and a blade; FIG. 5B is a partially exploded back view ofthe blade shaft assembly of FIG. 5A;

FIG. 6A is a perspective view of the blade of FIG. 5A; FIG. 6B is afront view of the blade of FIG. 5A; FIG. 6C is a back view of the bladeof FIG. 5A; FIG. 6D is a cross-sectional view of the blade of FIG. 5Ataken along line E-E of FIG. 5A;

FIG. 7A is a longitudinal side cross-sectional view of a shaft portionof the cutter of FIG. 2A with the blade in the retracted configuration;FIG. 7B is a longitudinal side cross-sectional view of the shaft portionof the cutter of FIG. 2A with the blade in the extended configuration;

FIG. 8A is a perspective view of another embodiment of a blade for thecutter of FIG. 2A; FIG. 8B is a cross-sectional view of the blade ofFIG. 8A taken approximately along line B-B of FIG. 8A;

FIG. 9A is a perspective view of another embodiment of a blade for thecutter of FIG. 2A; FIG. 9B is a cross-sectional view of the blade ofFIG. 9A taken approximately along line C-C of FIG. 9A;

FIG. 10 is a view of a guide wire inserted to cross a joint of a firstbone and a second bone at a procedure site, and a set of dilatorsmounted over the guide wire; in FIGS. 10-22 the first and second bonesand the joint are depicted in cross-section in order to view thecomponents of the invention in situ;

FIG. 11 is a view of the guide wire and dilators of FIG. 10, with acannula inserted over the guide wire and dilators and docked into thefirst bone;

FIG. 12 is a view of the cannula of FIG. 11, with an impactor mounted onan end of the cannula;

FIG. 13 is a view of the cannula of FIG. 11, with an support strutsattached to the cannula;

FIG. 14A is a view of the cannula of FIG. 11, with a sleeve partiallyreceived in a bore of the cannula; FIG. 14B is a longitudinalcross-sectional view of the cannula, guide wire and sleeve of FIG. 14A;

FIG. 15 is a view of the cannula and sleeve of FIG. 14A, with a drillinserted through the cannula and sleeve, and a passageway drilled acrossthe joint;

FIG. 16A is a view of the cannula and sleeve of FIG. 14A, with thecutter of FIG. 2C inserted into the cannula and sleeve, the cutter bladein the extended configuration, and a circular cavity cut into the firstbone and second bone across the joint; FIG. 16B is a close-up view ofthe distal end of the sleeve and cutter of FIG. 16A, also showing acutting radius r of the cutter and a diameter d of the cavity; FIG. 16Cis a cross-sectional view of the cutter shaft portion, cannula andsleeve of FIG. 16A cutting a cavity in a sacro-iliac joint;

FIG. 17 is a view of the cannula, sleeve and cavity of FIG. 16A, with asuction tool inserted through the cannula and sleeve and into thecavity;

FIG. 18 is a view of the cannula, sleeve and cavity of FIG. 16A, with agraft funnel mounted in the cannula, a tamp inserted through the graftfunnel, and bone graft material in the cavity;

FIG. 19 is a view of the cannula, sleeve, cavity and bone graft materialof FIG. 18, with a drill inserted through the cannula and sleeve, andanother passageway drilled across the joint deeper into the second bone;

FIG. 20 is a view of the cannula, sleeve, cavity, bone graft materialand passageway of FIG. 19, with a guide wire installed though thepassageway and into the second bone and a length gauge mounted on thecannula;

FIG. 21 is a view of the cannula, sleeve, cavity, bone graft material,guide wire passageway and of FIG. 19, with the fusion device of FIG. 1implanted in the first bone and second bone, across the joint;

FIG. 22 is a view of the joint and fusion device of FIG. 21, with aguide brace mounted over the guide wire and the supplementary screwinserted in the first bone and second bone, across the joint;

FIG. 23A is a side view of the fusion device of FIG. 1; FIG. 23B is aperspective view of the fusion device of FIG. 1; FIG. 23C is across-sectional view of the fusion device of FIG. 1, taken along lineF-F in FIG. 23A; FIG. 23D is an exploded view of the fusion device ofFIG. 1;

FIG. 24 is a perspective view of the cannula of FIG. 11;

FIG. 25 is a perspective view of the sleeve of FIG. 14A;

FIG. 26 is a perspective view of the length gauge of FIG. 20;

FIG. 27 is a perspective view of the graft funnel of FIG. 18;

FIG. 28 is a perspective view of the tamp of FIG. 18;

FIG. 29 is a perspective view of an alternate embodiment of a fusiondevice screw-type fastener;

FIG. 30 is a perspective view of another alternate embodiment of afusion device screw-type fastener;

FIG. 31 is a perspective view of another alternate embodiment of afusion device screw-type fastener;

FIG. 32 is a perspective view of another alternate embodiment of afusion device screw-type fastener;

FIG. 33 is a perspective view of another alternate embodiment of afusion device screw-type fastener;

FIG. 34 is a perspective view of another alternate embodiment of afusion device nail-type fastener;

FIG. 35 is a perspective view of another alternate embodiment of afusion device nail-type fastener;

FIG. 36 is a perspective view of another alternate embodiment of afusion device nail-type fastener;

FIG. 37 is a perspective view of another alternate embodiment of afusion device nail-type fastener;

FIG. 38A is a view of an axial computer tomographic (CT) scan of apelvis, showing an idealized trajectory for a sacro-iliac joint implant,and measurement segments along the trajectory; and FIG. 38B is a blackand white line tracing of the bony anatomy of the CT scan of FIG. 38A,showing the idealized trajectory for a sacro-iliac joint implant, andthe measurement segments along the trajectory; and

FIG. 39 depicts a longitudinal axis of the screw member of FIG. 1, and awasher bore central axis of the washer of FIG. 1 at various degrees ofangulation with respect to the screw member longitudinal axis.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention relates specifically to systems and methods forfusion of a sacroiliac joint, and more generally to systems and methodsfor creating a cavity in a bone or joint. Those of skill in the art willrecognize that the following description is merely illustrative of theprinciples of the invention, which may be applied in various ways toprovide many different alternative embodiments. This description is madefor the purpose of illustrating the general principles of this inventionand is not meant to limit the inventive concepts in the appended claims.

The terms “front”, “side”, “back”, “upper” and “lower” are used hereinto identify a relative frame of reference to a particular device or anindividual element of a device. In alternate embodiments the front orupper side of a device or element may be established on any desired sideof the device or element.

According to a first aspect of the disclosure, an implant for providingcompression across a joint between a first bone portion and a secondbone portion, wherein a cavity is located within the joint between thefirst bone portion and the second bone portion, comprises: a screwmember having a screw head, and a screw body projecting distally fromthe screw head along a longitudinal axis to a screw distal end, thescrew body comprising a non-threaded lag zone and a threaded engagementzone, the lag zone extending from the screw head distally to theengagement zone, the engagement zone extending from the lag zone to thescrew distal end; and a washer member having a proximal side and adistal side, and a bore having a central bore axis; wherein the screwhead is received in the washer member, and the screw body projectsdistally from the washer member; and an implant fusion zone having alength which is measured from the distal side of the washer member to aproximal end of the screw engagement zone, wherein the length of theimplant fusion zone ranges from about 10 mm to about 37 mm.

Embodiments of this aspect of the disclosure may include one or more ofthe following features: The washer member further includes asemispherical capsule between the proximal side and the distal side, andthe screw head is received in the semispherical capsule to permitpolyaxial angulation of the washer member with respect to the screwmember. The permitted polyaxial angulation of the washer member centralbore axis with respect to the screw member longitudinal axis ranges fromat least −8 degrees to at least +8 degrees. An annular groove is formedbetween the screw head and the screw body, wherein the screw is smallerin diameter at the annular groove than at the lag zone or at the screwhead. The washer member is captive to the screw member. The screw membercomprises a central longitudinal bore extending from the screw head tothe screw distal end. The lag zone includes at least one fenestrationwhich opens into the central longitudinal bore. At least a portion ofthe fenestration is located within the implant fusion zone. An overalllength of the implant, measured from the distal side of the washer tothe screw distal end when the washer central bore axis is coaxial withthe screw member longitudinal axis, ranges from about 40 mm to about 110mm. The implant comprises at least two different surface finishes. Thelag zone and at least a portion of the threaded engagement zone comprisea roughened surface finish; the distal end of the screw member comprisesa non-roughened surface finish; and the screw head and washersemispherical capsule comprise a non-roughened surface finish. Theimplant is a sacro-ilial fusion implant, wherein the joint is asacroiliac joint, the first bone portion is an ilium, the second boneportion is a sacrum, and the cavity is located between the ilium and thesacrum; wherein, when the implant is installed across the sacroiliacjoint, the distal side of the washer member is in contact with anexterior surface of the ilium, the implant fusion zone extends at leastpartially across the sacroiliac joint and the cavity, and the threadedengagement zone is at least partially embedded in the sacrum.

According to a second aspect of the disclosure, a method for compressinga joint between a first bone portion and a second bone portion, whereina cavity is located within the joint between the first bone portion andthe second bone portion, comprises providing an implant comprising ascrew member having a screw head and a screw body projecting distallyfrom the screw head along a longitudinal axis to a screw distal end, thescrew body comprising a non-threaded lag zone and a threaded engagementzone; and a washer member having a proximal side and a distal side,wherein the screw head is received in the washer member; wherein theimplant further comprises a fusion zone having a length which ismeasured from the distal side of the washer member to a proximal end ofthe screw engagement zone, wherein the length of the implant fusion zoneranges from about 10 mm to about 26 mm; inserting the screw bodyengagement zone through the first bone portion and into the cavity;engaging the screw body engagement zone with the second bone portion;positioning at least a portion of the lag zone within the cavity;rotating the screw member to compress the joint; and angling the washermember with respect to the screw member to permit maximum surfacecontact of the distal side of the washer member with the first boneportion.

Embodiments of this aspect of the disclosure may include one or more ofthe following features and/or methods: The lag zone comprises afenestration opening into a central longitudinal bore, and the methodfurther comprises filling the fenestration with bone graft material.Filling the cavity with bone graft material. The washer member comprisesa bore having a central bore axis. Angling the washer member withrespect to the screw member comprises angling the washer member centralbore axis with respect to the screw member longitudinal axis within therange of at least −8 degrees to at least +8 degrees. The implant is asacro-ilial fusion implant and the joint is a sacro-iliac joint, andwherein the first bone portion is an ilium, and the second bone portionis a sacrum, and the cavity is located between the ilium and the sacrum.Positioning the fusion zone to extend into cavity, wherein the fusionzone crosses the first bone portion and extends into cavity. Positioningthe fusion zone to contact the second bone portion.

According to a third aspect of the disclosure, a system for compressinga joint between a first bone portion and a second bone portion comprisesan instrument for excising a cavity between the first bone portion andthe second bone portion, the instrument having a handle and a bladeassembly, wherein the blade assembly is movable between a retractedconfiguration and an extended configuration relative to an instrumentlongitudinal axis to define a cutting radius; and an implant forproviding compression across the first bone portion, the cavity, and thesecond bone portion to fuse the joint, wherein the implant comprises: ascrew member having a screw head, and a screw body projecting distallyfrom the screw head along a longitudinal axis to a screw distal end, thescrew body comprising a lag zone and a threaded engagement zone; awasher member having a proximal side and a distal side, wherein thescrew head is received in the washer member, and the screw body projectsdistally from the washer member; and an implant fusion zone is definedto extend from the distal side of the washer member to a proximal end ofthe screw threaded engagement zone.

Embodiments of this aspect of the disclosure may include one or more ofthe following features: The lag zone is non-threaded and extends fromthe screw head distally to the engagement zone, and the engagement zoneextends distally from the lag zone to the screw distal end. The screwbody comprises a central longitudinal bore extending from the screw headto the screw distal end, and the lag zone comprises a fenestrationopening into the central longitudinal bore. The washer member comprisesa semispherical capsule between the proximal side and the distal side,and the screw head is received in the semispherical capsule to permitpolyaxial angulation of the washer member with respect to the screwmember. The washer comprises a bore having a central bore axis, whereinthe permitted polyaxial rotation angulation of the washer member centralbore axis with respect to the screw member longitudinal axis ranges fromat least −8 degrees to at least +8 degrees. An overall length of theimplant, measured from the distal side of the washer to the screw distalend when the washer central bore axis is coaxial with the screw memberlongitudinal axis, ranges from about 40 mm to about 110 mm. The lengthof the implant fusion zone ranges from about 10 mm to about 37 mm. Theimplant is a sacro-ilial fusion implant, and the joint is a sacroiliacjoint, the first bone portion is an ilium, the second bone portion is asacrum, and the cavity is excised between the ilium and the sacrum. Whenthe implant is installed across the sacroiliac joint, the distal side ofthe washer member is in contact with an exterior surface of the ilium,the implant fusion zone extends at least partially across the sacroiliacjoint and the cavity, and the threaded engagement zone is embedded inthe sacrum. An outer diameter of the cavity is determined by theinstrument cutting radius, and the maximum outer diameter of the implantis less than the cavity outer diameter.

FIG. 1 illustrates a natural sacroiliac joint fused by methods of theinvention. The sacroiliac joint 2 comprises the meeting of a sacrum 5and an ilium 6. According to methods of the invention disclosed herein,a cavity 20 is created between the sacrum 5 and the ilium 6, and may befilled with bone graft material 15. A fusion device 550 is implantedacross the joint 2 to provide compression and fuse the joint. The fusiondevice may be sized to extend through the ilium 6, across the joint 2and cavity 20, and into the sacrum 5, extending through the corticalbone 4, the sacral ala 7, and into the sacral vertebrae 9 of the sacrum5. It is appreciated that the instrumentation and methods disclosedherein may also be applied to provide fusion in any other joint, or toprovide fusion between two or more bones or bone portions.

FIGS. 2-9B disclose a cutting instrument, herein referred to as a cutter100, which may be used to create the cavity 20 in the joint 2. In otherembodiments of the method, cutter 100 may applied to create a cavitywithin a bone or bones, and/or across a joint. Referring to FIGS. 2A-2C,cutter 100 outwardly comprises a handle portion 102, a shaft portion104, and a blade portion 106. In use by a practitioner, the handleportion 102 may be gripped and moved to direct the shaft and bladeportions 104, 106 to a specific area such as a bone or joint, andmanipulated to deploy a blade to create a cavity in the bone or joint.The cutter comprises a proximal end 110 and a distal end 112 with acutter central longitudinal axis 114 extending therebetween.

Referring to FIGS. 2A-3, the handle portion 102 comprises a handle 120and a knob 122, and has a distal end 124 and a proximal end 126. Theshaft portion 104 comprises an outer tubular member or outer tube 134which extends distally from the handle portion 102 and terminates at thedistal end 112. Housed within the outer tube 134, and handle 120 is ablade shaft 140. The blade shaft 140 extends from the proximal end 110of the cutter, through the knob 122, handle 120 and outer tube 134. At adistal end of the blade shaft 140, a blade 150 is modularly andpivotably connected to the blade shaft 140 via a blade retainer 142. Theblade may also be referred to as a cutting member, or a decorticator. Inalternative embodiments, the blade may be monolithic with the bladeshaft or may be permanently attached to the blade shaft.

Referring to FIG. 2A, handle 120 includes a handle outer surface 260which can include gripping features 262 and indicia 264. Indicatorwindows 266 allow viewing of markings 176 from either side of the handle120. Similarly, the knob 122 includes a knob outer surface 270 which caninclude gripping features 272 and indicia.

Referring to FIGS. 4A, 4B and 4C, additional detail of the blade shaft140 is shown. Blade shaft 140 extends between a proximal end 160 and adistal end 162 along a shaft central longitudinal axis 164. When theblade shaft 140 is assembled with the outer tube and handle, the shaftcentral longitudinal axis 164 is coaxial with the cutter centrallongitudinal axis 114. In an embodiment, the blade shaft 140 may becannulated throughout, having a central bore 165. The blade shaft caninclude a proximal handle portion 180, a shaft 182, and a distalattachment portion 184. The blade shaft may include an engagementfeature 166 which engages with the knob 122, forming an actuationmechanism which controls extension and retraction of the blade 150.

As seen in FIGS. 4A and 4C, the handle portion 180 of the blade shaft140 includes a longitudinal section 183 which is generally rectangularin cross-section. The rectangular section engages with the handle 120 toprevent rotation of the blade shaft 140 relative to the handle 120.Indicia, which may take the form of the markings 176, are present on theblade shaft and positioned to be visible through a window in the handle120, allowing a practitioner to determine the diameter of the cavitybeing excised by the blade 150. At the distal end 162 of the blade shaft140, an attachment feature 178 protrudes distally allowing forattachment of the blade holder 142. The attachment feature 178 is shapedas a boss 186 having an undercut 188 and paired angled projections orears 190 to retain the blade holder 142. In another embodiment, theblade holder may connect to the blade shaft in another connectionmechanism, or may be permanently connected. In another embodiment, theblade 150 may be directly connected to the blade shaft 140.

With reference to FIGS. 2A and 3, outer tube 134 includes a tubular body280 extending between a proximal end 282 and a distal end 284. Thedistal end 284 of the tubular body 280 terminates in a distal end face290. Adjacent the distal end 284 is a notch 292 which may be viewedfluoroscopically to ascertain the position of the distal end 112 of thecutter 100 during a procedure. A blade window 294 functions as anopening to allow the blade 150 to protrude out of the tubular member forcutting procedures. A ramped surface 296 opposite and interior to theblade window 294 guides the blade 150 as it is urged out of the window294, guiding the blade to project laterally relative to the cutter axis114. When the blade 150 is fully projected away from the cutterlongitudinal axis 114 and out the window 294, the ramped surface 296functions as a stop to prevent further distal movement of the blade 150and hold it rigid relative to the cutter 100.

The connections between the blade shaft 140, blade holder 142 and blade150 are illustrated in FIGS. 5A and 5B. In the embodiment depicted,blade holder 142 may be snapped on and off of blade shaft 140. Bladeholder 142 includes a first or shaft end 300 and a second or blade end302. The shaft end 300 is U-shaped, comprising a pair of connectedsidewalls 304, 306 separated by a gap 308 shaped to receive the bladeshaft boss 186. Each sidewall terminates in a tab 305, 307. When theblade holder is snapped on to the blade shaft 140, the boss 186 isreceived in the gap 308, and tabs 305, 307 are engaged under the angledprojections, or ears, 190.

The blade end 302 includes a receiver boss 310 having a bore 312, thebore extending perpendicular to the longitudinal axis of the bladeholder 142. The blade end 302 terminates in a curved or ramped surface316 sloping to an apex 314. When the cutter 100 is properly assembledand the blade 150 is fully extended out of the blade window, as seen forexample in FIG. 7B, the ramped surface 316 provides structural supportand rigidity, and provides a physical stop to rotation of the bladerelative to its holder 142 during cutting steps, and a physical stop tomovement of the blade 150 relative to the cutter 100 during cuttingsteps. A pin or may pivotably connect the blade 150 to the blade holder142 via extending through the bore 312. In another embodiment, anotherpivotable connection may connect the blade 150 to the blade holder 142or directly to the blade shaft 140.

Referring to FIGS. 6A-6D, the blade 150 includes a proximal orattachment end 330, a distal end 332, and a curved blade body 334extending therebetween along a blade length. The attachment end 330includes first and second extensions 336, 338 which project proximallyfrom the blade body 334, and include bores to receive a connecting pin.The body extensions 336, 338 are separated by a gap 339 shaped toreceive the receiver boss 310. The curved blade body 334 may be reducedin its width relative to the first and second extensions 336, 338, asseen in FIGS. 6B and 6C.

The blade body 334 is shaped as a loop, looping from the extensions 336,338 at a blade front side 340 on a blade first leg 341, forming aU-shaped terminal curve 342 at the distal end 332, back to theextensions 336, 338 at a blade back side 344 on a blade second leg 343.The blade 150 may also be described as lasso-shaped or banana-shaped. Acurved void 346 extends from the extensions 336, 338 to the terminalcurve 342, separating the blade first leg 341 from the blade second leg343. The curved void 346 provides passage for bone fragments and othermaterials moved by or encountered by the blade 150 during use. A bladefirst side 348 extends between the first extension 336 and the distalend 332, and a blade second side 350 extends between the secondextension 338 and the distal end 332, opposite the blade first side 348.Thus, the blade first side 348 includes portions of both the first andsecond legs 341, 343, as does the blade second side 350. The first andsecond legs 341, 343 may be parallel to one another, separated by thewidth of the void 346.

A furrow or blade relief 352 is recessed into the blade body, the bladerelief 352 continuous from the blade front side 340 on first leg 341onto the blade back side 344 on the second leg 343. Opposite the bladerelief 352 is a rounded ridge 353, which is also continuous from thefirst leg 341 on to the second leg 343, and forms the boundary of thecurved void 346. Put another way, the blade front side 340 and the bladeback side 344 each include a concave curvature along their respectivelengths, the concave curvature centered along the midline of the bladelength to reduce the contact area at the cutting surface and thus reducethe drag forces on the blade. Opposite the concave curvature is a convexcurvature. The blade first side 348 terminates laterally in a firstcutting edge 356, and the blade second side 350 terminates laterally ina second cutting edge 358 which projects opposite from the first cuttingedge. Thus, a curved cutting edge having an open ended U shape is formedon either side of the blade 150, enabling cutting to occur whether thecutter 100 is rotated clockwise or counter-clockwise. The blade 150 isbilaterally symmetrical relative to a longitudinally extending midline,generally demarcated by the center of the blade relief 352, between thefirst side 348 and the second side 350. A first sloped surface 360slopes from the first cutting edge 356 to the ridge 353, and a secondsloped surface 362 slopes from the second cutting edge 358 to the ridge353. The sloped surfaces 360, 362 may facilitate movement of severedmaterial toward the void 346 and away from the cutting edge to preventclogging during operation of the cutter 100. In another embodiment ofthe invention, the blade body may include a single cutting edge,enabling unidirectional cutting when the cutter 100 is rotated in onedirection. In another embodiment of the invention, rotation of thecutter 100 may be limited to a single direction.

Viewed in cross-section as in FIG. 6D, the blade legs 341, 343 are eachgenerally V-shaped. The cutting edges 356, 358 form the opposing lateraltips of the V, and the blade relief 352 and ridge 353 form the bottom ofthe V. Because the blade is looped, a cross-section of the entire bladeto include both blade legs results in twin V shapes which areback-to-back, or facing away from one another, and separated by the void346, as seen in FIG. 6D. It is also noted that each leg 341, 343 iscurved in at least two planes: from the first side 348 to the secondside 350, and from the proximal end 330 to the distal end 332. The shapeof each leg may be described as an elongated hyperbolic paraboloid, oras an elongated saddle shape. The blade relief provided by the shape ofthe blade reduces friction as the blade is rotated during a cuttingprocedure.

In the embodiment shown, the blade 150 is a monolithic entity composedof a rigid material, in order to provide sufficient rigidity duringcutting processes to cleanly cut through softer tissues such ascartilage, and harder materials such as cancellous bone, andparticularly, cortical bone. The blades disclosed herein may be composedof stainless steel. The blade 150 may be provided in a variety of sizes,varying in length, width, curvature, and/or thickness. A practitionermay select the appropriate sized blade for the patient and attach theblade to the cutter 100.

The blade shaft 140, blade holder 142 and blade 150 form a bladeassembly 155. The blade assembly 155 is modular and may be inserted andremoved from the cutter 100 as needed, for example to change blades. Theblade 150 and blade holder 142 may be provided in a variety of shapes,lengths, widths, curvatures and/or angles in order to create the desiredsize and shape of cavity when the cutter is deployed. By way ofnon-limiting example, the radius of curvature between the proximal 330and distal 332 ends of the blade 150 vary, as may the radius ofcurvature between the first and second cutting edges 356, 358, indifferent embodiments of the blade. The length of the blade 150 fromproximal 330 and distal 332 ends may vary, as may the depth between thefront side 340 and the back side 344, and/or the width between thebetween the first side 348 and the second side 350. The blade holder 142may be provided in a variety of lengths, and the angle of the rampedsurface 314 may vary.

FIGS. 7A and 7B are cross-sectional views of the shaft 104 and blade 106portions of cutter 100. During assembly of the cutter, the outer tube134 may be attached to the handle portion 102 to form a housing assembly145. The blade 150 may be attached to the blade holder 142; in someembodiments the blade and blade holder may be provided pre-assembled.The blade holder 142 is snapped to the blade shaft 140 as describedherein. The blade assembly 155 can be inserted into the housing assembly145 in a proximal to distal approach, with the blade 150 leading throughknob 122 and handle 120. The indicia on the blade shaft 140 and on thehandle 120 can provide guidance as to the proper orientation of theblade shaft about its longitudinal axis 164 as the blade assembly 155 isinserted. When the blade assembly 155 is fully inserted and in theretracted or stowed configuration, the blade 150 rests inside bladewindow 294 at the distal end of the housing assembly 145, and the blade150 is generally longitudinally aligned to extend along the cutter axis114.

To employ the cutter 100 at a procedure site, the cutter distal end 290is positioned at the site. To extend the blade 150 from the stowedconfiguration, torque may be applied to knob 122 to rotate it in a firstdirection such as clockwise, wherein the knob 122 engages the engagementfeature 166 of blade shaft 140 to translate the blade assembly 155distally along the device axis 114. As the blade assembly 155 movesdistally, the blade 150 is projected laterally away from device axis 114and out of window 294, biased by contact with ramped surface 296, whichfunctions as a curved guide surface during blade extension. The bladedistal end 332 moves along curved guide path 370 as the blade exits thewindow. The indicia 176 are visible through the handle window 266 andmay indicate the current cutting diameter of the instrument. When adesired cutting diameter is displayed, rotation of the knob is ceased,and to perform a cutting step the entire cutter 100 may be rotated aboutits longitudinal axis 114 by applying torque to the handle, allowing theleading cutting edge 356 or 358 to cut through the bone or othermaterial surrounding the exposed blade 150. The cutting step may form acircular cavity in the procedure site. After the cutting step, the knob122 may again be actuated to further extend the blade laterally out thewindow 294, and the cutting step may be repeated. Extension andretraction of the blade may be ceased at any point along the curved path370.

It is noted that during the cutting step, the blade 150 is essentiallyimmobilized relative to the cutter 100; independent movement of theblade 250 is prevented. If the blade 150 is less than fully extended,the blade 150 is rigidly held between the bone or joint being cut andthe ramped surface 296; rotational movement of the blade 150 in concertwith rotational movement of the cutter 100 is permitted but movement ofthe blade 150, including pivotal, axial and rotational, relative to theshaft 140 and cutter 100 is prevented. When the blade 150 is fullyextended, the blade 150 is rigidly held between the opposing curvedsurfaces 316 and 296 in a locked position; rotational movement of theblade 150 in concert with rotational movement of the cutter 100 ispermitted but movement of the blade 150, including pivotal, axial androtational, relative to the shaft 140 and cutter 100 is prevented.

When fully extended, the longitudinal curvature of blade 150 may matchthe curvature of guide path 370. By way of example, in the embodimentdepicted in FIG. 7B, the concave curvature of the ramped surface 296matches the convex curvature of the blade second leg 343 and bladeholder 142 when the blade 150 is fully extended out of the blade window,to provide structural support and rigidity, and to provide a physicalstop to independent movement of the blade 150 relative to the shaft 140and cutter 100. The blade extension and cutting steps may be repeated asdesired to create a cavity of a selected diameter at the procedure site.When cutting is completed, the knob 122 may be turned in a seconddirection such as counter-clockwise to translate the blade shaft 140proximally and retract the blade 150 into the window 294, and the cuttermay be withdrawn from the procedure site. Optionally, the cutter 100 maybe inserted axially deeper into the procedure site and redeployed todeepen the circular cavity or create another cavity. Optionally, thecutter 100 may be rotated less than 360° to create a cavity that is lessthan a full circle.

The cutter 100 described herein may be used in a procedure to fuse asacro-iliac joint. In a procedure, the cutter 100 may be deployed tocreate a cavity in the cartilage at the joint between the sacrum and theilium, and/or in the hard cortical bone matter of the sacrum and/orilium. Bone graft material may be inserted into the cavity, and a fusiondevice may be implanted across the joint to compress and fuse the joint.

Referring to FIGS. 8A-9B, alternative embodiments of a blade for cutter100 are shown. FIGS. 8A and 8B disclose a blade 200 having a proximal orattachment end 201, and a distal or working end 202, and a curved bladebody 204 extending therebetween along a blade length. An attachmentportion 203 is proximate the proximal end 201. The description of thefeatures of the attachment end of blade 150 also applies to blades 200and 250. The blade body 204 is shaped as a loop, looping from attachmentend 201 at a blade front side 206 on a blade first leg 208, forming aU-shaped terminal curve 210 at the distal end 202, back to theattachment end 201 at a blade back side 212 on a blade second leg 214.The blade 200 may also be described as lasso-shaped or banana-shaped. Acurved void 216 extends from the attachment portion 203 to the terminalcurve 210, separating the blade first leg 208 from the blade second leg214. The curved void 216 provides passage for bone fragments and othermaterials moved by or encountered by the blade 200 during use. A bladefirst side 218 extends between the attachment end 201 and the distal end202, and a blade second side 220 extends between the attachment end 201and the distal end 202, opposite the blade first side 218.

The blade body 204 is flat on a continuous outer surface 222 formed bythe front side 206 of first leg 208, around the terminal curve 210, andthe back side 212 of second leg 214. The blade first side 218 terminateslaterally in a first cutting edge 224, and the blade second side 220terminates laterally in a second cutting edge 226 which projectsopposite from the first cutting edge. Thus, a curved cutting edge havingan open ended U shape is formed on either side of the blade 200,enabling cutting to occur whether the cutter 100 is rotated clockwise orcounter-clockwise. The blade 200 is bilaterally symmetrical relative toa longitudinally extending midline, generally demarcated by the midlinecenter of the continuous outer surface 222, between the first side 218and the second side 220. In cross-section as in FIG. 8B, the first leg208 and second leg 214 are generally triangular, resulting in twintriangular shapes which are apex-to-apex, or facing away from oneanother, and separated by the void 216. The other features of blade 150also apply to blade 200, including the void, and the sloped surfacesextending from the cutting edges toward the void.

FIGS. 9A-9B disclose another alternate embodiment of a blade for usewith cutter 100. The description, form and features of blade 150 applyto blade 250, with the exception of the cutting edges. Blade 250includes first 252 and second 254 cutting edges which are broken up byscallops or serrations 256. The serrations 256 may vary in size alongdifferent portions of the blade 250, and may extend inward as far as thelongitudinally extending midline of the blade. When deployed in cutter100, the serrations 256 may facilitate cutting through hard corticalbone material.

A method of fusing a joint is set forth below. It is appreciated thatalthough the method described is for a sacro-iliac joint, the method canbe applied to any joint, or to fusion of any two bones or bone portions.In addition, the instruments and/or methods described herein may beapplied to other procedures, including at least: intramedullaryosteotomies for limb-lengthening, derotation, and/or malunionprocedures; spinal disc space joint preparation for arthrodesis,arthroplasty and/or other procedures; and subtalar joint preparation forankle fusion. The cutter 100 may be advantageously used to cut both softcancellous bone and hard cortical bone.

Referring to FIGS. 10-27, systems and methods for preparing a jointspace and implanting a fusion implant are shown. The method may includeone or more of the following steps described below. It is understoodthat in certain embodiments of the method, the steps may or may not beperformed in the order set forth below, one or more of the steps may beomitted, one or more of the steps may be repeated, and/or additionalsteps may be performed. In other embodiments of the invention, thesystems and methods described herein may be used to fuse two boneportions, or two bones.

FIGS. 10-22 include a stylized cross-sectional depiction of a meeting ofan ilium 6 and a sacrum 5 at a sacro-iliac joint 2. At the joint 2, theportion of the ilium depicted may include primarily hard cortical bone.The sacrum 5 is depicted as having three strata; hard cortical sacralbone 4, the sacral ala 7 and the sacral vertebral body 9. It isappreciated that the natural joint 2 between the ilium 6 and sacrum 5undulates, as do the strata of the sacrum 5, with the natural anatomy ofthe bones; in the figures they are depicted as straight lines forclarity.

Referring to FIG. 10, in a step a guide wire is introduced into aprocedure site, in the example shown a sacro-iliac joint 2 between asacrum 5 and an ilium 6. In the embodiment shown, the guide wire isintroduced through the ilium, and into the joint space, so that the tipof the guide wire is in the joint space. The guide wire may comprise aguide line, guide pin, k-wire, or another guiding line known in the art.The guide wire may create an access passageway 8 through skin, muscleand other tissues from outside the patient to the sacro-iliac joint. Inone embodiment, a first guide wire comprising a 2 mm k-wire may beintroduced, removed, and a larger diameter guide wire 400 is introducedthrough the access passageway 8 created by the first guide wire. Theguide wire may be positioned so that a tip 402 of the larger diameterguide wire 400 protrudes through the ilium 6 across the joint 2 and intothe bone 4 of the sacrum 5. In one embodiment, the guide wire 400 may bea 3.2 mm k-wire. Following introduction of the guide wire 400, inanother step one or more cannulated dilators 404, 406, 408 may besequentially introduced over a proximal end 401 of the guide wire 400toward the procedure site, to further increase the diameter of theaccess passageway 8. In the example shown, three dilators are introducedsequentially, in ascending diameter size, over the guide wire 400. Eachdilator may be inserted concentrically over the guide wire and previousdilator(s) until a distal end of the dilator, for example distal end 410of dilator 408 contacts the ilium 6. In another embodiment of themethod, one or more steps of the method may be performed withoututilizing guide wires. In another embodiment of the method, acomputerized navigation system may be used to guide the instrumentationand steps of the system.

Referring to FIGS. 11, 14A, and 24, in another step an access cannula420 is introduced over the guide wire 400 and dilator(s). The accesscannula 420 includes a proximal end 422 and a distal end 424, with aperipheral wall 426 extending therebetween, surrounding an internal bore425. The cannula 420 may include one or more distally projecting teeth428 which may protrude into the ilium 6 to dock the cannula to the iliumand stabilize the position of the cannula. The cannula 420 may furtherinclude one or more brackets 430 or other attachment features to connectto stabilizing elements such as wires or struts. The brackets 430 may bespecifically shaped and/or angled to hold the stabilizing elements in adesired alignment. A portion of the peripheral wall 426 includesinternal threading 432, and one or more access ports 434 may be formedin the peripheral wall 426. Upon introduction into the procedure site,the teeth 428 may protrude several millimeters into the ilium, but inthe embodiment shown, preferably do not extend into the joint 2.

Referring to FIG. 12, in another step an impactor 440 may be connectedto the proximal end 422 of the cannula 420 to drive the teeth 428 intothe ilium and more securely fix the cannula in place. A mallet or othertool (not shown) may be used to apply axial force to the impactor 440.

Referring to FIG. 13, following the docking of the cannula into theilium, in another step one or more stabilizing guide wires 444 may beconnected to the brackets 430 and distal ends 445 of the guide wires 444introduced into the ilium 6, to further stabilize the position of thecannula 420 for subsequent steps of the method. When the cannula 420 issatisfactorily positioned and stabilized, the dilator(s) 404, 406, 408may be proximally withdrawn from the cannula, over the guide wire 400.

Referring to FIGS. 14A, 14B and 25, in another step a sleeve 450 isintroduced over the guide wire 400 and into the proximal end of thecannula 420. The sleeve 450 includes a proximal end 452, a distal end454 and a sleeve body 456 surrounding a longitudinal sleeve bore 455. Arim 458 encircles the sleeve body 456, and a portion of the sleeve bodyincludes external threading 460 for engagement with the access cannula420, forming an adjustment mechanism with the cannula. The sleeve body456 may include a proximal section 462, a neck 464 and a distal section466. The diameter of the sleeve bore 455 may decrease from the proximalsection 462 to the distal section 466, tapering in the neck 464. Aflange 469 projects outwardly from the distal section 466 and maystabilize the distal section with respect to the access cannula 420.

The sleeve 450 may include indicia 468 so that as the sleeve 450 isengaged with the access cannula 420, a precise distance to the cannuladistal end 424, and thus the procedure site, may be achieved. Thecombined axial length of the sleeve 450 and cannula 420 may be adjustedalong a continuum by rotation of the sleeve 450. This adjustabilityallows precise placement of the cutter blade 150 at the joint 2, and mayprevent over-insertion of the cutter 100 or other instrumentation. Atleast one ball detent may be received in a cannula access port 434, andinteract with a groove 463 formed on the exterior of the sleeve body 450to provide tactile indication of the extent of the sleeve rotation. Thereduced inner diameter of the sleeve distal section 466 may preciselytarget instrumentation such as cutter 100 toward the procedure site.

Referring to FIG. 15, in another step a drill 470 is introduced over theguide wire 400 and through the sleeve bore 455 and cannula bore 425. Afirst passageway 18 is drilled through the ilium 6, across the joint 2,and into the sacrum, and replaces the access passageway 8. After thedrilling step, the guide wire 400 may be withdrawn from the accesscannula 420. Suction may be applied to remove material from the firstpassageway 18.

Referring to FIGS. 16A and 16B, in another step the cutter 100 isintroduced, with the shaft portion 104 inserted through the sleeve 450,cannula 420, and first passageway 18. The cutter distal end 112 maycontact the sacrum 5, and the blade 150 within blade window 294 arepositioned past, or distal to, the distal end 424 of the cannula 420.During the introduction step, the blade 150 is in the retractedconfiguration, so that it is contained within a diameter envelope of theouter tube 134. The handle distal end 124 may contact the rim 458 of thesleeve, limiting the insertion depth of the cutter 100. The sleeve 450may be rotated as needed to adjust the depth of the cutter distal end112. Fluoroscopy may be utilized as desired to visualize notch 292 andblade window 294, allowing precise placement of cutter 100 relative tothe joint 2 at the procedure site.

When the cutter shaft 104 and blade 106 portions are at the desiredlocation, and the blade portion 106 is distal to the cannula distal end424, in one or more steps knob 122 is rotated to deploy the cutter blade150 laterally. During initial deployment, only a small portion of theblade 150 may project laterally out of the blade window, the bladedistal end 332 extending to a first deployed distance r, measured as thedistance from the cutter longitudinal axis 114 to the blade distal end332, perpendicular to the axis 114. The deployed distance represents theradius of a circle which may be cut by the cutter blade. Thepractitioner may check the deployed distance by reading the indicia 176visible in the indicator window 266. In embodiments of the device, theindicia 176 indicate the diameter of a circular cavity cut by thedevice. In embodiments of the device, the diameter cut by the cuttingdevice 100 may range from 2 mm to 70 mm, and the cutting radius ordeployed distance r may range from 1 mm to 35 mm. Blades 150 of varyinglengths may be provided to attain the range of cutting diametersdisclosed herein.

In another step, torque is applied to the handle 120 to rotate theentire cutter 100 about its longitudinal axis, thus sweeping the blade150 in a circular path to perform a first cut. The cutting edge 356 or358 at the leading side of the blade 150 cuts into the surrounding boneand/or other tissue. Fragments of the bone and/or tissues are severedfrom the joint and are urged toward the void 346, the leading slopedsurface 360 or 362 facilitating movement of the tissue fragments awayfrom the cutting edge and toward the void 346. The blade 150 cuts acavity having a diameter determined by the distance between the cutterlongitudinal axis and the blade distal end 332 at its deployed distance,or r. After the first cut, the knob 122 may again be rotated relative tothe handle 120 to further extend the blade laterally to a seconddeployed distance. The entire cutter 100 may be rotated again to performa second cut of a larger diameter, thus increasing the diameter of thecavity. These steps may be repeated as needed until the desired diametercavity 20 is created. FIG. 7B illustrates the blade 150 at a fullydeployed or fully extended configuration. At the fully extendedconfiguration, the blade 150 is held essentially immobile relative tothe cutter 100 by contact with the opposing curved surfaces 296 and 316,which act as stops to lock the blade in its extended position. At lessthan the fully extended configuration, the extended blade 150 is heldrigid by contact with the ramped surface 296 and contact with the boneor other tissue against which the blade is deployed.

Referring to FIG. 17, in one or more steps suction may be deployed inbetween cutting steps, or at other points during the proceduresdescribed herein, as needed to clear debris from the cavity and/orinstrument. To deploy suction, the cutter 100 or other instrument may bewithdrawn from the cannula 420. A suction tool 470 may be inserted,until an opening 472 of the suction tool 470 is at a desired location inthe cannula 420 or cavity 20, or pathway 18. The suction tool 470 may beconnected to a suction source, and suction is applied until the debrisis removed. Fluid may be applied during the suction process. In otherembodiments, means for suction may be integrated into cutter 100,eliminating the need for a separate suction tool.

After the cavity 20 of a desired or selected diameter is created, bonegraft material and/or other substances may be introduced into thecavity. With reference to FIGS. 18 and 27, a graft funnel 480 may beused to guide bone graft material into the cavity 20. The graft funnelincludes a funnel portion 482 and a conduit 484. A pair of openings 483on opposite sides at the distal end of the conduit 484 allow movement ofthe graft material out of the conduit. A plug 485 in the distal end ofthe conduit includes guide surfaces that divert the graft material outof the opposing openings 483. In a graft insertion step, the graftfunnel may be inserted to extend through the sleeve 450 and cannula 420with the distal end of the conduit 484 opening into the cavity 20. Graftmaterial 15 is inserted into the funnel portion 482. A tamp 486 may beused to push the graft material distally through the conduit 484 towardthe plug 485, out the side openings 483 and into the cavity 20. The tampmay include a handle 487, a shaft 488 and a distal tamp face 489. Inanother embodiment, a tamping member with a solid distal tamp face maybe coupled to the blade holder 142 of the cutter 100 and deployed byrotation of the knob 122 to push the graft material through the conduit484 and into the cavity 20. During a graft insertion step, the funnel480 may be selectively rotated to ensure that graft material exits theopenings 483 into all or selected parts of the cavity 20.

Referring to FIG. 19, in another step of the method a tunnel may bedrilled through the packed bone graft and across the cavity to preparefor insertion of a fusion device. Prior to drilling the hole, a dilatorsuch as dilator 404 may be reintroduced into through sleeve 450 intocannula 420, to provide a guide for a guide wire. The guide wire 400 mayalso be reintroduced, and inserted through the ilium 6, the cavity 20and graft 15, and into the sacrum 5, extending through the hard corticallayer 4, the sacral ala 7 and into the sacral vertebral body 9. A drill490 is introduced over the guide wire 400 to drill a second passageway28 also extending through the bone graft and cavity and into the sacrum5, to provide a passage for the fusion screw implant. In anotherembodiment of the method, both passageways 18 and 28 may be drilledprior to cutting the graft cavity 20 with the cutter 100.

As shown in FIGS. 20 and 26, in another step of the method a lengthgauge 510 can be used to determine the proper length for a fusionimplant. Length gauge 510 includes a support member 512 having a distalend 514, a proximal end 516, and a bore 515; and further includes agauge 518 and set screw 520. Set screw 520 may include a ball detent.The gauge 518 is partially cannulated, having a blind bore 519 shaped toreceive the proximal end 401 of guide wire 400, the blind bore having anend surface 521. The gauge 518 also includes a blind groove 22. Whenassembled for use, the gauge 518 is received in bore 515 of the supportmember 512. Set screw 520 extends through an opening in the supportmember 512 and into the groove 522. To measure for proper implantlength, the screw length gauge 510 is mounted on to cannula 420, withthe distal end 514 of the support member 512 resting on the proximal end422 of the cannula. The guide wire 400 proximal end 401 is received inthe blind bore 519 of the gauge 518. The gauge 518 may be adjusted untilthe end surface 521 of the blind bore 519 rests on the proximal end 401of the guide wire 400. The proper implant length may then be indicatedby indicia 524 on the gauge 518, read where the gauge 518 intersects thesupport member proximal end 516.

As shown in FIGS. 1, and 21-23D, in another step of the method aproperly sized fusion implant 550 may be implanted into the preparedcavity 20, crossing the cavity and joint 2 and engaging the sacrum 5 andilium 6. The fusion implant 550 includes a screw member 552 and a washermember 554. The screw member 552 includes a head 566 and a distal tip568 with a screw body 564 extending therebetween, extending along ascrew longitudinal axis 557. The head 566 is preferably spherical andhas a spherical center point 569. Engagement features 567, for example ahex feature as seen in FIGS. 23B and 23C, are present in the head 556for connection with insertion and/or removal instrumentation. The screwmember 552 may include a bore or lumen 551 extending along itslengthwise dimension to allow for introduction over the guide wire 400,and may include one or more fenestrations, or apertures 556 which openinto lumen 551 for graft packing and bone through-growth. The lumen 551may be concentric about the axis 557. A self-tapping threaded engagementzone 558 is distal to a non-threaded lag zone 560. An annular lip 559projecting from the screw body 564 may provide resistance tounintentional screw withdrawal, and may provide additional compressionwhen the implant 550 is inserted across a joint. An undercut, or annulargroove 561 may encircle the screw member 552 at the junction of thescrew head 566 and screw body 564. The screw member 552 is smaller indiameter at the annular groove 561 than at the lag zone 560 or at thescrew head 566. A distal annular surface 563 encircles the screw body564 between the lip 559 and the annular groove 561, and is slopedrelative to a transverse plane of the screw member.

As shown in FIGS. 22 and 23A-D, the lag zone 560 may be non-threaded andcylindrical. The lack of exterior threading on the lag zone 560 permitscompression of the joint 2 between the engagement zone 558, and thescrew head 566 and/or washer 554 as the implant 550 is implanted acrossthe joint 2 and into the sacrum 5. In an embodiment, the diameter of thelag zone 560 is 10 mm; in another embodiment, the diameter of the lagzone 560 is 12 mm. In other embodiments of the disclosure, the diameterof the lag zone can range between about 6 mm and about 14 mm. In thecontext of the diameter of the lag zone, “about” is defined as +/−1 mm.In an embodiment, the outer diameter of the washer is about 24 mm, andtherefore a maximum outer diameter of the implant is about 24 mm. In thecontext of the outer diameter of the washer, “about” is defined as +/−8mm. In an embodiment, the maximum outer diameter of the implant is lessthan the diameter of the prepared cavity 20. In another embodiment, themaximum outer diameter of the implant is greater than the diameter ofthe prepared cavity 20.

The screw member 552 may include internal threads 562 or other featuresfor engagement with implantation and/or removal instrumentation. Uponimplantation, the engagement zone 558 may be at least partially embeddedin the sacrum 5, extending into the body of the sacral vertebra 9; andthe lag zone 560 may cross the ilium 6, joint 2, cavity 20, and canextend into the sacrum 5. The washer 554 abuts the ilium 6. The screwmember 552 may be sized so that the lag zone 560 is positioned to extendthrough the ilium, and the engagement zone 558 extends into the body ofthe sacral vertebra 9 upon implantation, permitting engagement in theregion with improved bone quality including higher bone density.

The washer 554 includes an upper or proximal side 570, a lower or distalside 572, and a semispherical capsule 553 positioned between the upperand lower sides. The semispherical capsule 553 has a spherical centerpoint 571 and may be concavely curved, and circumscribes a bore 555defining a central bore axis 582. When properly assembled with the screwmember 552, the semispherical capsule 553 may retain the head 566 of thescrew member 552, and the screw body 554 protrudes distally from thebore 555. The head 566 may be recessed below the upper side 570 of thewasher. An inner diameter of the washer 554 at the lower side 572 may beapproximately equal to the outer diameter of the screw member at the lip559. In the context of the inner diameter of the washer 554 at the lowerside 572 and the outer diameter of the screw member at the lip 559,“approximately” is defined as the inner diameter of the washer 554 atthe lower side 572 being equal to, or up to 5% smaller than, the outerdiameter of the screw member at the lip 559. Thus when the screw head566 is properly assembled within the washer member 554 as in FIG. 23,the washer member is captive to the screw member, the projecting lip 559preventing unintentional disassembly of the washer member from the screwmember 552.

The implant 550 further includes a fusion zone 565, which is defined asextending from the distal side 572 of the washer to the proximal end ofthe screw member engagement zone 558, as shown in FIG. 23. The fusionzone 565 is non-threaded, and is a zone of compression and long-termfixation of the joint, between the washer and the threaded engagementzone.

A study which documented the anatomical dimensions of the sacro-iliacjoint of 50 subjects was used to determine the overall length ofembodiments of the implant 550, the length of the fusion zone 565, andthe diameter of the screw member engagement zone 558. Computerizedtomography (CT) scans of the subjects were measured, providingdimensions of the iliac width, the sacro-iliac joint space width, thesacral alar width, and the width of the body of the sacral vertebraalong an ideal sacro-iliac implant trajectory 690, as shown in an axialpelvis CT in FIGS. 38A and 38B. The sacral ala is generally known tohave lower bone mineral density (BMD), while the body of the sacralvertebra is known to have higher BMD. Some studies have shown a 2×increase in BMD in the body of the sacral vertebra when compared to thesacral ala. In addition, the length of a “safe zone” 688 at the boundarybetween the sacral ala and sacral vertebral body, and perpendicular tothe trajectory 690, was measured. The safe zone length extends betweenthe boundaries (normal to the SI joint) of an area through which asacral fixation implant may be inserted without impinging on neuralstructures or soft tissues. The safe zone dimension may be used todetermine the diameter of the screw member engagement zone 558. Theideal implant trajectory 690 passes normal to the SI joint and crossesthe safe zone 688 at the midpoint of the safe zone, and ultimatelyanchors in the denser sacral vertebral body 9. Such a trajectory normalto the SI joint will provide the maximum compression during fusion, andpassing through the middle of the safe zone allows the least risk to thepatient.

Referring to FIGS. 38A and 38B, segment 692 is the iliac width, segment694 is the sacro-iliac joint space width, segment 696 is the sacral alarwidth, segment 698 is the sacral vertebral body width, and 688 is thesafe zone length. Summary results of the study are presented in Table 1below.

TABLE 1 Average measurements along Sacro- Iliac Implant Trajectory, inmm Iliac Joint Alar Body Safe Zone Width Width Width Width LengthAverage 15.19 5.75 31.15 37.24 17.9 Max 22.9 14.5 42.9 46.2 22.2 Min 9.62.1 20.7 25 13.9 St. Dev. 2.1

The average depth of the joint from the ilial outer surface (ilial widthplus joint width) is 21 mm. Based on these study results, the length ofthe fusion zone 565, measured with the washer in a neutral, coaxiallyaligned position relative to the screw member, was designed to be 23 mmfor all screw members greater than or equal to 60 mm long, and 19 mm forall screw members less than 60 mm long, in order to provide optimal fit,engagement with high quality bone, and fusion, in the sacro-iliac joint.The shorter fusion zone on shorter screw members facilitates havingsufficient remaining threaded length in the engagement zone for bonepurchase. However, in other examples the length of the fusion zone 565may be directly proportional to the screw length according to thisformula: FZ=mL+B, where FZ=fusion zone length, m=slope, L=screw length,and B=intercept.

The overall length of the screw member 552 may range between about 40 mmand about 110 mm. In the context of the overall length of the screwmember 552, “about” is defined as +/−2 mm. Screw members 552 may beavailable in 5 mm increments between 40 mm and 110 mm lengths, althougha screw member of any intermediate length may also be provided. Thelength of the fusion zone 565 may range from about 10 mm to about 37 mmlong. In the context of the length of the fusion zone 565, “about” isdefined as +/−2 mm. For screw members 552 greater than or equal to 60 mmlong, the fusion zone 565 may be 23 mm long. For screw members 552 lessthan 60 mm long, the fusion zone 565 may be 19 mm long.

In an embodiment, the diameter of the screw member engagement zone 558is 12 mm. This diameter is based on the safe zone measurements in Table1; a 12 mm diameter allows 2 mm on either side of the screw memberengagement zone 558, while remaining within the safe zone averagemeasurement of 17.9 mm.

The semispherical connection between the head 566 and the washer member554 permits polyaxial orientation of the screw member 552 relative tothe washer member 554. The reduced diameter of the screw member at theannular groove 561 with respect to the screw body 564 enables a greaterrange of motion for the washer member than if the screw member diameterwere not reduced. In addition, the angled distal annular surface 563 ofthe screw body 564 enables a greater range of motion for the washermember than if the distal annular surface were flat, or perpendicular tothe longitudinal axis 557. The washer/screw connection provides at least+/−8 degrees of angulation of the washer member relative to the screwmember, as defined by the position of the central bore axis 582 of thewasher bore 555 relative to the longitudinal axis 557 of the screwmember. The range of motion of the central bore axis 582 relative to thelongitudinal axis 557 of the screw member is conical in shape, with theapex of the cone at the spherical center point 569 of the screw head566. When the screw head 566 is properly assembled within the washercapsule 553, the spherical center point 569 is coincident with thespherical center point 571 of the washer capsule 553.

FIG. 39 depicts the relationship of the central bore axis 582 of thewasher bore 555 relative to the longitudinal axis 557 of the screwmember at various degrees of angulation. In the neutral position, forexample as seen in FIGS. 23A and 23C, the washer bore axis 582 iscoaxial with the screw member axis 557, and the washer member is angledat 0 degrees relative to the screw member. In an embodiment, thewasher/screw connection permits at least +/−8 degrees of angulation ofthe washer member relative to the screw member. In other embodiments,the washer/screw connection permits +/−9 degrees, +/−10 degrees, +/−11degrees, +/−12, +/−13 degrees, +/−14 degrees, +/−15 degrees, +/−16degrees, +/−17 degrees, +/−18 degrees, +/−19 degrees, +/−20 degrees,+/−21 degrees, +/−22 degrees, +/−23 degrees, +/−24 degrees, +/−25degrees, +/−26 degrees, +/−27 degrees, +/−28 degrees, +/−29 degrees, or+/−30 degrees of angulation of the washer member relative to the screwmember.

The implant 550 may include one or more surface finishes to promoteengagement with bone. The lag zone 560 and/or the threaded engagementzone 558 may be grit-blasted and/or include a hydroxyapatite coating ora non-hydroxyapatite coating to provide a roughened surface finish. Thescrew member tip 568 may have a non-roughened surface finish for easierinsertion into bone. The screw head 566 and washer capsule 553 may eachhave a non-roughened surface finish to permit easy angulation of thewasher with respect to the screw head. For example, in an embodiment,the screw head 566 and body 564 distal to and including the lip 559 maybe glass bead finished or polished to provide the non-roughened finish;the body 564 distal of the lip 559 to the tip 568 may be titaniumanodized, and optionally coated with hydroxyapatite coating, to providethe roughened surface finish; and the tip may be glass bead blasted orpolished to produce the non-roughened surface finish.

In a method of implantation, an implant inserter 530 may be used in astep to place and engage the fusion implant 550 in the prepared site, asshown in FIG. 21. The inserter 530 includes a handle portion 532, ashaft portion 534 and an engagement tip 536. Some or all of the inserter530 may be cannulated. The engagement tip 536 may include features toengage with the engagement features 567 of the head 566 to enableinsertion and rotation of the screw member 552. The inserter 530 mayfurther include a ratchet system or other mechanisms for implantrotation or deployment. In a method of use, the screw member 552 may becoupled with the washer member 554, with the head 566 received in thewasher capsule 553 and the screw body 564 protruding distally. Theimplant 550 may be placed over the proximal end 401 of the guide wire400, with the screw member tip 568 extending distally toward the jointor procedure site. The inserter engagement tip 536 is coupled to theimplant 550, and the inserter may be moved to urge the implant 550distally along the guide wire 400 toward the prepared site. As theimplant 550 crosses the joint 2 and the cavity 20 and into passageway28, the threaded engagement zone 558 may engage in the sacrum 5. The tip568 and a portion of the engagement zone 558 may be embedded in thesacral vertebral body 9, which has a higher bone density than the sacralala and may therefore provide better long-term biological fixation. Theinserter 530 may be rotated or otherwise deployed to rotate the implant550 and secure it in the bone. Once the washer member 554 abuts theilium 6, the implant 550 may be further rotated to provide compressiveforce across the joint 2. The washer member 554 may be angled relativeto the screw member 552 to permit maximum surface contact of the distalside of the washer member with the ilium. The fusion zone 565 extendsfrom the exterior ilium bone surface, through the ilium, and through thecavity and joint, and may contact the sacrum. In the fully inserted andsecured position such as shown in FIGS. 1, 21 and 22, the apertures 556are aligned with and open to the joint 2 and the cavity 20, allowing forgraft distribution into and through the implant 550, and bonethrough-growth.

With regard to FIG. 22, in another step of the method a secondary orauxiliary screw 580 may be deployed to extend across the joint 2 tofurther stabilize the joint. Auxiliary screw 580 may be fully threadedand self-tapping. A guide brace 590 may be mounted over guide wire 400to assist in determining a trajectory for auxiliary screw 580. The guidebrace 590 includes a bracket 592, which may be angled. A guide wire 596is guided through the bracket 592 and into the procedure site, at anoblique angle relative to the longitudinal axis of the implant 550 andguide wire 400. The auxiliary screw 580 is introduced over guide wire596 along the trajectory and through the ilium 6 and into the sacrum 5,crossing the joint 2. In another embodiment of the method, more than onefusion implant 550 may be implanted. In other embodiments of the method,no auxiliary screw 580 may be deployed, or multiple auxiliary screws maybe deployed. In other embodiments of the method, an auxiliary screw 580may be implanted to extend parallel to the primary fusion implant 550,and a guide brace with a parallel bracket may be used.

FIGS. 29-37 disclose alternate embodiments of fastener members which maybe included in a fusion implant such as implant 550. Any of the fastenermembers may be coupled with washer member 554 to form a fusion implant,or may be combined with other washer members, or may be usedindividually. Any of the fastener members disclosed herein may includesurface roughening, grit-blasting, or coatings on all or a portion ofthe fastener member to promote bone engagement. Any of the fastenermembers may be cannulated, and may include fenestrations or windows forgraft distribution or bone ingrowth.

Referring to FIGS. 29-33, alternate embodiments of screw-type fastenermembers are disclosed. Fastener member 600 includes head 602, tip 603,threaded portion 604, lag portion 606, and annular grooves 608. Fastenermember 600 is a combination fastener, the threaded portion 604 having adouble lead tip transitioning to a single lead toward the head 602. Thethread diameter of the threaded portion 604 may taper moving from thelag portion 606 toward the tip 603. Fastener member 610 includes head612, tip 613, threaded portion 614, lag portion 616, and annular grooves618. Fastener member 610 is a double lead screw with dual threads ofincreasing height moving from the tip 613 toward the head 612. Fastenermember 620 includes head 622, tip 623, threaded portion 624, lag portion626, and annular grooves 628. Fastener member 620 is a single lead screwhaving tall threads to support cancellous bone. Fastener member 630includes head 632, tip 633, threaded portion 634, lag portion 636, andannular grooves 638. Fastener member 630 is a double lead screw havingdual height threads which provide additional joint compression when themember 630 is implanted across a joint. Fastener member 640 includeshead 642, tip 643, threaded portion 644, lag portion 646, and annulargrooves 648. Fastener member 640 includes double lead threading whichmay allow faster installation than fasteners with single lead threading.The annular grooves 608, 618, 628, 638, 648 are tapered towards therespective fastener head to provide resistance to fastener withdrawal.The annular grooves may also function as compression bands to grab boneand provide added compression across a joint as they are driven intobone. The lag portions 606, 616, 626, 636, 646 may be proportioned toaccommodate the width of a bone they are implanted in, such as an ilium.

Referring to FIGS. 34-37, alternate embodiments of nail-type fastenermembers are disclosed. Fastener members 650, 660, 670 and 680 may beused as supplementary or auxiliary implant to a fusion device such as550, to provide additional compression across a joint, and resistance tojoint rotation. Fastener member 650 includes a head 652 and tip 654 withspiral shaft 656 extending therebetween. The spiral shaft 656 includes afast hexagonal spiral which provides compression across the joint.Fastener member 660 includes a head 662 and tip 664 with spiral shaft666 extending therebetween. The spiral shaft 666 includes a slowhexagonal spiral which provides compression across the joint. Fastenermember 670 includes a head 672 and tip 674 with spiral shaft 676extending therebetween. The spiral shaft 676 includes a slow squarespiral which provides compression across the joint. Fastener member 680includes a head 682 and tip 684 with shaft 686 extending therebetween.The shaft 686 comprises annular grooves which taper toward the head 682,and which provide compression across the joint and resistance towithdrawal.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. Above aredescribed various alternative examples of systems and methods for jointfusion and for creating a cavity within a bone or joint. It isappreciated that various features of the above-described examples can bemixed and matched to form a variety of other combinations andalternatives. Not every instrument described herein may be used in aprocedure such as a joint fusion. For example, in a method of fusing ajoint, the steps of using the cutter instrument may be optional. Inother embodiments of the method, the sleeve and/or cannula may beoptional. The instruments described herein may be used in otherprocedures not described herein. As such, the described embodiments areto be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

The invention claimed is:
 1. A method for compressing a joint between afirst bone portion and a second bone portion, wherein a cavity islocated within the joint between the first bone portion and the secondbone portion, the method comprising: undercutting the cavity with acutter; positioning an implant proximate the joint, the implantcomprising: a screw member having a screw head and a screw bodyprojecting distally from the screw head along a longitudinal axis to ascrew distal end, the screw body comprising a threaded engagement zoneand a non-threaded lag zone comprising an opening into a centrallongitudinal bore; and a washer member having a proximal side and adistal side; wherein the implant further comprises a fusion zone havinga length extending from the distal side of the washer member to aproximal end of the threaded engagement zone; inserting bone graftmaterial into the central longitudinal bore; inserting the threadedengagement zone through the first bone portion and into the cavity;engaging the threaded engagement zone with the second bone portion;positioning at least a portion of the non-threaded lag zone within thecavity such that the opening is in the cavity to allow the bone graftmaterial to move from the central longitudinal bore into the cavity;rotating the screw member to compress the joint; and angling the washermember with respect to the screw member to permit maximum surfacecontact of the distal side of the washer member with the first boneportion.
 2. The method of claim 1, wherein the non-threaded lag zonecomprises a fenestration on which the opening is formed.
 3. The methodof claim 1, wherein: the proximal side of the washer member comprises asemispherical capsule; and the screw head is received in thesemispherical capsule.
 4. The method of claim 1, wherein the washermember comprises a bore having a central bore axis; wherein angling thewasher member with respect to the screw member comprises angling thewasher member central bore axis with respect to the screw memberlongitudinal axis within the range of at least −8 degrees to at least +8degrees.
 5. The method of claim 1, wherein the implant is a sacro-ilialfusion implant and the joint is a sacro-iliac joint, and wherein thefirst bone portion is an ilium, and the second bone portion is a sacrum,and the cavity is located between the ilium and the sacrum.
 6. Themethod of claim 1, wherein the cutter consists essentially of a singleblade.
 7. The method of claim 1, wherein the length of the implantfusion zone ranges from about 10 mm to about 37 mm.
 8. A method forcompressing a joint between a first bone portion and a second boneportion, wherein a cavity is located within the joint between the firstbone portion and the second bone portion, the method comprising:undercutting the cavity with a cutter; positioning an implant proximatethe joint, the implant comprising: a screw member having a screw headand a screw body projecting distally from the screw head along alongitudinal axis to a screw distal end, the screw body comprising anon-threaded lag zone and a threaded engagement zone; and a washermember having a distal side and a proximal side with a recess, whereinthe screw head is received in the recess of the washer member; whereinthe implant further comprises a fusion zone having a length extendingfrom the distal side of the washer member to a proximal end of thethreaded engagement zone; inserting the threaded engagement zone throughthe first bone portion and into the cavity; engaging the threadedengagement zone with the second bone portion; positioning at least aportion of the non-threaded lag zone within the cavity; rotating thescrew member to compress the joint; and angling the washer member withrespect to the screw member to permit maximum surface contact of thedistal side of the washer member with the first bone portion.
 9. Themethod of claim 8, wherein: the non-threaded lag zone comprises anopening into a central longitudinal bore; the method further comprisesinserting bone graft material into the central longitudinal bore; andpositioning at least a portion of the non-threaded lag zone within thecavity comprises positioning the opening in the cavity to allow the bonegraft material to move from the central longitudinal bore into thecavity.
 10. The method of claim 8, wherein: the recess comprises asemispherical capsule; and the screw head has a semispherical shapecomplementary to the semispherical capsule.
 11. The method of claim 8,wherein the washer member comprises a bore having a central bore axis;wherein angling the washer member with respect to the screw membercomprises angling the washer member central bore axis with respect tothe screw member longitudinal axis within the range of at least −8degrees to at least +8 degrees.
 12. The method of claim 8, wherein theimplant is a sacro-ilial fusion implant and the joint is a sacro-iliacjoint, and wherein the first bone portion is an ilium, and the secondbone portion is a sacrum, and the cavity is located between the iliumand the sacrum.
 13. The method of claim 8, wherein the cutter consistsessentially of a single blade.
 14. The method of claim 8, wherein thelength of the implant fusion zone ranges from about 10 mm to about 37mm.
 15. A method for compressing a joint between a first bone portionand a second bone portion, wherein a cavity is located within the jointbetween the first bone portion and the second bone portion, the methodcomprising: undercutting the cavity with a cutter consisting essentiallyof a single blade; positioning an implant proximate the joint, theimplant comprising: a screw member having a screw head and a screw bodyprojecting distally from the screw head along a longitudinal axis to ascrew distal end, the screw body comprising a non-threaded lag zone anda threaded engagement zone; and a washer member having a proximal sideand a distal side, wherein the screw head is received in the washermember; wherein the implant further comprises a fusion zone having alength extending from the distal side of the washer member to a proximalend of the threaded engagement zone; inserting the threaded engagementzone through the first bone portion and into the cavity; engaging thethreaded engagement zone with the second bone portion; positioning atleast a portion of the non-threaded lag zone within the cavity; rotatingthe screw member to compress the joint; and angling the washer memberwith respect to the screw member to permit maximum surface contact ofthe distal side of the washer member with the first bone portion. 16.The method of claim 15, wherein: the non-threaded lag zone comprises anopening into a central longitudinal bore; the method further comprisesinserting bone graft material into the central longitudinal bore; andpositioning at least a portion of the non-threaded lag zone within thecavity comprises positioning the opening in the cavity to allow the bonegraft material to move from the central longitudinal bore into thecavity.
 17. The method of claim 15, wherein: the proximal side of thewasher member comprises a semispherical capsule; and the screw head hasa semispherical shape complementary to the semispherical capsule. 18.The method of claim 1, wherein the washer member comprises a bore havinga central bore axis; wherein angling the washer member with respect tothe screw member comprises angling the washer member central bore axiswith respect to the screw member longitudinal axis within the range ofat least −8 degrees to at least +8 degrees.
 19. The method of claim 15,wherein the implant is a sacro-ilial fusion implant and the joint is asacro-iliac joint, and wherein the first bone portion is an ilium, andthe second bone portion is a sacrum, and the cavity is located betweenthe ilium and the sacrum.
 20. The method of claim 15, wherein the lengthof the implant fusion zone ranges from about 10 mm to about 37 mm.